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This is your brain on exercise

A profile MRI of the brain with color shaded areas corresponding to areas of increased gray matter volume in active people. The blue crosshairs point to increased volume in the hippocampus with more calories burned per week. The hippocampus is the key memory and learning center of the brain.

Seniors who fit in the most daily physical activity – from raking leaves to dancing – can have more gray matter in important brain regions, researchers reported on Monday.

The scientists have images that show people who were the most active had 5 percent more gray matter than people who were the least active. Having more little gray brain cells translates into a lower risk of Alzheimer’s disease, other studies have shown.

“People really want to know what they can do to reduce their risk of Alzheimer’s disease,” said Dr. Cyrus Raji of the University of California in Los Angeles, who presented his team’s findings to a meeting of the Radiological Society of North America.

Raji’s team looked at the records of 876 adults, who were recruited into a larger study on heart health starting in 1989. They all got magnetic resonance imaging (MRI) brain scans in 1998 and 1999, when they were on average 78 years old, and filled out detailed questionnaires on exercise and other types of activity.

Most of them were a little overweight – with a body mass index or BMI of 27. People with BMIs above 25 are considered overweight and at 30 they are considered clinically obese.

The researchers found a huge difference in the amount of activity people reported. They were asked about everything from cycling to yard work, dancing and bicycle riding.

“The most active burned 3,434 calories per week (an extra 500 calories per day on average) compared to those in the bottom percentile who only burned 348 calories per week [through activities],” Raji said. “The most active had 5 percent more gray matter volume than the least active. That's a big number when you think about the tremendous biological forces that have to be at work for brain volume to change at all.”

And the MRIs showed the differences were in areas of the brain like the hippocampus, which is heavily damaged in Alzheimer’s disease.

“By strengthening this area, an active lifestyle can reduce risk for Alzheimer's,” Raji said. "Virtually all of the physical activities examined in this study are some variation of aerobic physical activity, which we know from other work can improve cerebral blood flow and strengthen neuronal connections.”

Money is limited for new medical research, so the UCLA team went through the records from another study -- that explains why some of the data is old. "This is the largest study of its kind that has ever been done," Raji said.

But even older data can be a gold mine for researchers. To log exercise, the volunteers wrote down all the activities they could remember over a two-week period. Some went back and filled out questionnaires five years later, so Raji's team could make some comparisons.

"We found that individuals who increased calories burned over five years also had more gray matter volume," Raji said.

Raji isn't sure how some people only managed to burn off 348 extra calories a week, but said they may have been ill or even bedridden.

When they looked in more detail at the surveys, the researchers noted that it was the people who managed to work exercise into their daily lives who racked up the most weekly calories. So unless people enjoy standard “exercise” such as running, they should find something they like and are likely to stick to, said Raji.

“No pharmaceutical drug on the market has been shown to have these effects on the brain -- not a single drug,” said Raji. And exercise is available to anyone. “And it doesn’t cost anything,” he said.

In the first 10 years of the study, 97 people developed Alzheimer’s, and just about a quarter of them were in the top 25 percent of exercisers. Raji said the disease was detected very early in this study because the volunteers were being studied so intensely. “Most had not yet been diagnosed by their primary care physicians,” he said.

Now the team is going to go through the surveys to see if the people who had the most gray matter were the least likely to develop Alzheimer’s – or if the brain disease progressed more slowly in those with the most gray matter. And they want to follow up with as many of the volunteers as possible to see how they have fared.

“I really do believe that we have strong evidence that physical activity can be a way to reduce the risk of Alzheimer’s disease,” Raji said.

How many calories can you burn doing various activities? The Centers for Disease Control and Prevention has a calculator here. An hour of dancing can burn 330 calories an hour while walking burns about 280 calories an hour.